Zoonoses constitute more than 60% of all known infectious diseases and 75% of emerging infectious diseases. Their impact is not monitored, prevented and treated in an integrated way. The efficacy of therapeutic interventions for zoonotic diseases is deemed to be comparable across species with scientifically valid results originating from a range of animal experiments. Ethical obligations limit the number of animals used in experiments as well as reduce repetition of studies. The evidence based on randomized controlled trails and systematic reviews for the effectiveness of health care interventions is often inconclusive. Subjecting human volunteers to risk in the absence of scientifically valid results from animal experiments is unethical. The One Health concept is a comparative, clinical approach directed towards zoonoses which present challenges to research workers and clinicians. Optimal health for all--One Health--should be underpinned by ethically conducted research in animals or humans and the results should be complementary to both.